23.11.5: Crusting disease Flashcards
What is a crust and how useful is it diagnostically?
Crust: dried exudate, containing blood / serum / scales / pus. Colloquially known as a scab.
* Occasionally a primary lesion but more commonly secondary e.g. to scaling, pustular or ulcerative disease.
* Very common but not diagnostically useful in isolation
Top differential for this case
This dog has hypothyroidism and superficial pyoderma
What is the most common cause of crusts in the dog?
Superficial pyoderma
First steps in approach to the animal with crusts
- Rule out ectoparasites: using routine tests such as skin scrapes, combing, trichogram, treatment trial
- Rule out bacterial pyoderma: using cytology of primary lesion if pos, otherwise impression smear from skin under crust. Also consider dermatophytosis (esp in cats) -> use Wood’s lamp, consider culture.
-
Further investigations if lesions remain
* Biopsy a good idea; most likely to be diagnostic if the secondary infection is cleared first
* Don’t dislodge the crust if you want to biopsy it; trim the hair with scissors but otherwise no prep
* Consider requesting special stains esp re microorganisms
Primary differential?
This is sarcoptic mange until proven otherwise
Primary differential?
Feline atopic skin syndrome (FASS) / FFA
Fleas also a major consideration
Primary differential?
Facial DLE / mucocutaneous pyoderma
* These are clinically indistinguishable even on biopsy
* Must treat as pyoderma first
* If no response, consider resistance, or that it is DLE (autoimmune)
Diseases that present primarily as crusting
- Pemphigus foliaceus
- Canine juvenile sterile granulomatous dermatitis and lymphadenitis (a.k.a. juvenile cellulitis, puppy strangles)
- Squamous cell carcinoma / solar dermatitis
- Feline acne
- Calcinosis cutis
- Superficial necrolytic dermatitis (hepatocutaneous syndrome)
- Facial dermatitis of Persians
True/false: pad disease is a common finding with pyoderma.
False
Pad disease is not seen with pyoderma -> this rings autoimmune bells
What is your primary differential in this case? Do you cytological findings support this? What would you need to do to confirm your diagnosis?
- On cytology there are acantholytic keratinocytes (large “fried egg” cells, somtimes in rafts) and neutrophils
- This is very suggestive of pemphigus foliaceus
- Biopsy would be needed to confirm diagnosis
What findings can you see on cytology? What disease process are they suggestive of and how does this come about?
Acantholytic keratinocytes - large “fried egg” cells, sometimes in rafts
* These are keratinocytes who become detached from their friends, and they have no keratinised into rigid structures
* Suggestive of pemphigus foliaceus
Signalment for canine pemphigus foliaceus
- Most common autoimmune skin disease in dogs
- Seen in middle aged to older dogs (can occur at any age)
- Probably more common in males than females
- Strong breed dispositions: Akitas, Chows, Cocker Spaniels, Dachshunds, Labradors, English Bulldogs, Shetland Sheepdogs
Pathogenesis of canine pemphigus foliaceus
- Autoimmune (mainly IgG) response to desmosomal proteins especially desmocollin 1 - this is mainly expressed in superficial layers of epidermis so lesions fairly superficial
- Usually not too delibitating; very rare pemphigus vulgaris where lesions are much deeper
- Usually considered idiopathic but can occasionally be triggered by UV, and some drugs e.g. flea products
Clinical signs of canine pemphigus foliaceus
- Usually presents as bilaterally symmetrical crusting disease
- Start as pustules (larger and with erythematous margins cf pustules) but these are transient hence we see crusts / erosions
- Lesions can occur anywhere but head / pinnae involved in 80% of cases
- ± pruritus
- ± mildly unwell / pyrexia
How can secondary pyoderma complicate a diagnosis of canine pemphigus foliaceus?
- Secondary pyoderma with pemphigus foliaceus is common and confusing
- There is then a partial response to the treatment of pyoderma
If you treat a pyoderma but it is unresponsive to a reasonable treatment option, what disease should be on your differential list?
Pemphigus foliaceus
Treatment and prognosis of canine pemphigus foliaceus
Signalment and clinical signs of feline pemphigus foliaceus
- Less common than canine pemphigus foliaceus
- Wide range of ages of onset
- Giveaway: classic symmetrical crusting on paws
- Similar clinical signs to dogs: crusting disease ± pruritus ± pyrexia
- But also see affected claw folds (30% cases) and areolar skin
Diagnosis and treatment of pemphigus foliaceus in cats
As for the dog, except:
* Occasionally use oral dexamethasone (off label) in place of prednisolone
* ± adjunctive treatment: chlorambucil (NOT azathioprine in cats!), ciclosporin, topical steroids
* Need to monitor fructosamine when on steroids due to risk of inducing diabetes in cats
* Prognosis is better in cats than dogs
Canine juvenile sterile granulomatous dermatitis and lymphadenitis
Clinical signs of canine sterile granulomatous dermatitis and lymphadenitis
- Sterile pustules -> ulcers / draining tracts / crusts / hair loss and cellulitis affecting above areas
- Acute swelling of the muzzle, lips, eyelids
- Marked submandibular lymphadenopathy
- ± otitis externa
- ± pyrexia, depression, anorexia, joint pain
- (Rarely: nodules at other sites)
How can you differentiate between canine sterile granulomatous dermatitis and lymphadenitis and angioedema?
- In canine sterile granulomatous dermatitis and lymphadenitis the oedema does not pit and there are enlarged LNs - this does not hold true for angioedema
Signalment and presentation of canine juvenile sterile granulomatous dermatitis and lymphadenitis
- Sterile granulomatous condition affecting face, pinnae, ears and submandibular lymph nodes
- Aetiology unknown; possible immune dysfunction
- Breeds: especially Golden Retrievers, Labs, Dachshunds
- Age: usually puppies, occasionally adults
Diagnosis of canine juvenile sterile granulomatous dermatitis and lymphadenitis
- Signalment, history, clinical signs - very suggestive
- Important to rule out other conditions that may cause cellulitis e.g. Demodicosis, infections such as bacterial pyoderma and dermatophytosis
- Biopsy needed for confirmation: send for histopath and tissue culture
What would you expect to see on cytology of a lesion from a dog with canine juvenile sterile granulomatous dermatitis and lymphadenitis?
- Pyogranulomatous and apparently sterile inflammation
Treatment of canine juvenile sterile granulomatous dermatitis and lymphadenitis?
Signalment and clinical signs of feline SCC / solar dermatitis
Diagnosis, treatment and prevention of feline SCC / solar dermatitis
Characteristics and prognosis of canine SCC
Name and clinical presentation of the disease pictured
Feline acne
* Dark waxy scales / crusts on chin
* May be primary disorder but often secondary
* Often develops secondary to Malassezia, pyoderma, dermatophytosis, demodicosis, furunculosis
Treatment and control
Feline acne
Diagnosis and treatment
* Rule out demodicosis / dermatophytosis
* Address any secondary microbial infection
Control
* Maintenance management with topical keratinolytic products
What is the condition pictured and why does it arise?
Calcinosis cutis
What is the condition pictured? How does it present and what is it typically associated with?
Superficial necrolytic dermatitis
What is the prognosis for superficial necrolytic dermatitis?
Poor due to underlying disease that it is associated with
Clinical signs, diagnosis and treatment for superficial necrolytic dermatitis
Clinical signs and treatment of Idiopathic facial dermatitis of Persian cats
- Poorly understood condition; hard to control as we don’t know the cause
- Clinical signs: tightly adherent black scales and Malassezia dermatitis
- Treatment: anti-yeast therapy, ciclosporin ± prednisolone
- Guarded prognosis
A 6 y.o. DLH cat presents with bilaterally symmetrical crusting affecting the pinnae and face, and a caseous claw fold exudate affecting multiple digits.
What is your top differential diagnosis?
Pemphigus foliaceus
